Medical technologists perform laboratory tests to help physicians detect, diagnose, and treat diseases. The work of medical technologists is generally done under the supervision of a senior medical technologist, a clinical laboratory supervisor, or a physician who has specialized in diagnosing the causes and nature of disease. In laboratories, according to the American Society for Clinical Pathology, medical technologists work in five major areas: blood banking, chemistry, hematology, immunology, and microbiology.

Technologists in clinical practice ensure the quality of laboratory tests done for diagnosis. They may be responsible for interpreting the data and results and reporting their findings to the attending physicians. Many assist attending physicians in correlating test results with clinical data and recommending tests and test sequences. Medical technologists may have management and supervisory duties, including serving as laboratory manager, supervisor of lab sections, and staff supervisor over other technologists and laboratory personnel.

The specific tasks performed by medical technologists are determined by the kind of setting in which they work. Technologists employed by small laboratories conduct many kinds of tests, such as blood counts, urinalyses, and skin tests. They use microscopes to examine body fluids and tissue samples to determine the presence of bacteria, fungi, or other organisms. They prepare slides from sample tissues and body cells to ascertain, for example, whether an individual has developed cancer. Depending on the laboratory facilities and needs, they may operate highly sophisticated medical instruments and machines. They conduct research and maintain and make minor repairs to the instruments and equipment used in testing. Medical technologists employed in large laboratories are generally specialists.

Medical technology specialists normally have advanced degrees in their area of expertise. They are capable of handling sophisticated equipment and tests because of their education and training. They may be responsible for ordering, purchasing, maintaining, and repairing specialized equipment and instruments required for the laboratory tests. They design new laboratory procedures and establish or continue training and education of other employees in laboratory procedures and skills.

A chemistry technologist, or biochemistry technologist, tests specimens of blood, urine, gastric juices, and spinal fluid to detect the presence of chemicals, drugs, and poisons, as well as levels of substances made by the body, such as sugar, albumin, and acetone. This information may be used in the diagnosis of metabolic disease such as diabetes. Precise measurements are made with equipment maintained by the technologist.

A microbiology technologist, or bacteriology technologist, examines specimens for microorganisms, including viruses, fungi, parasites, and bacteria. It may be necessary to isolate and grow a specific organism to make a better identification for diagnosis. Treatment of a condition may depend on the results of testing various ways of dealing with the organism itself, before the patient can be treated.

A blood bank technologist, or immunohematology technologist, collects, types, and prepares blood and its components for transfusions. An immunology technologist examines elements of the human immune system and its response to foreign bodies. A cytotechnologist prepares slides of body cells and examines these cells under a microscope for abnormalities that may be the start of a cancerous growth. A molecular biology technologist performs complex protein and nucleic acid testing on cell samples

Clinical laboratory directors oversee the laboratory or the laboratory department. They usually hold an M.D., D.O., or Ph.D. They are responsible for the supervision of the technologists on the staff and for the quality of the work done. They may be in charge of sustaining the budget and determining the financial needs and responsibilities of the lab. They assign duties, hire and fire staff, and establish work rules and standards.

Clinical laboratory supervisors, or medical technology supervisors, manage the staff on a day-to-day basis. The supervisor assigns work schedules and assignments, reviews work and lab results, and may assist in training and continued education of the staff. The supervisor may also continue performing duties of the medical technologist. The chief medical technologist supervises the work of the entire laboratory operations, assigns duties, and reviews the reports and analyses.